It is generally well-known that an atmosphere which contains oxygen can cause surface cracking of conventional unsaturated rubber vulcanizates when subjected to repeated flexing in an oxygen-containing environment. Deterioration has been observed to occur when small "surface" cracks grow rapidly into deep, disruptive fissures. Fissures of this sort can significantly shorten the serviceable life of an elastomeric article made from a rubber vulcanizate.
The ongoing desire to prolong the useful life of elastomeric articles made from rubber--either natural or synthetic--is also well known.
U.S. Pat. No. 4,158,000 to Nagasaki et al., for example, discloses antidegradants for rubber, said to be useful for preventing heat-aging and flex-cracking. A mixture consisting essentially of specified percentages of 2,2,4-trimethyl-1,2-dihydroquinoline monomer, dimer thereof and more-highly-polymerized products are mentioned in the Nagasaki patent as providing rubber with such an antidegradant ingredient.
U.S. Pat. No. 2,400,500 to Gibbs, moreover, discloses various condensation products of 1,2-dihydroquinolines with diarylamines, said to be useful in preventing flex-cracking of rubber. Gibbs mentions in this patent that reacting an alipathic ketone with a primary aromatic amine to produce a 1,2-dihydroquinoline is known.
2,2,4-trimethyl-1,2-dihydroquinoline, a principal product resulting from the reaction of acetone and aniline, is a known useful antioxidant.
Many chemical antidegradants, principally based upon amine chemistry, have in fact been developed to arrest or otherwise delay the physical deterioration of articles made from cured elastomeric materials.
Current formulations for producing cured elastomeric articles typically include an insoluble form of sulfur, which prevents sulfur migration prior to vulcanization. Conversion of the insoluble form of sulfur to its soluble form, which is currently known to result in migration of soluble sulfur to the surface of an uncured rubber article, appears to be caused by the presence of amine-based antidegradants.
While mixtures which include 2,2,4-trimethyl-1,2-dihydroquinoline are known to prolong the useful life of elastomeric articles, which is desirable, the presence of 2,2,4-trimethyl-1,2-dihydroquinoline and its various forms are known to cause insoluble sulfur to convert to a soluble form of sulfur, which is undesirable.
For example, soluble sulfur is known to migrate to the surface of uncured rubber articles. Migration of this sort, called sulfur "bloom," is known to cause loss of "building tack."
The term "building tack" refers to certain adherence properties of uncured elastomeric materials such as rubber, particularly when such materials are produced as relatively-thin sheets and such sheets are thereafter layered and utilized in the fabrication of a tire.
Obtaining undesirable "building-tack" properties, using these sorts of elastomeric materials, can thus become a matter of concern.